1. Field of the Invention
The invention relates to a shaping apparatus for an extrusion system.
2. The Prior Art
A shaping device for an extrusion system is known from patent specification U.S. Pat. No. 4,181,487 A, which comprises at least one calibration apparatus with several plate-type sizing units arranged one after the other in the direction of extrusion. The individual sizing units arranged one after the other having a sizing orifice with several sizing surfaces to which the article being drawn through conforms in an engaging arrangement. These individual sizing units have end faces running in a direction more or less vertically and perpendicular to the sizing surfaces and channels are provided, recessed back from the sizing surfaces, in at least one of the end faces, which extend via a distribution channel to an accumulator channel. When the sizing units are placed side by side, these channels form a plurality of cavities, by means of which a pressure differential can be generated at various points of the article as it is fed through. These individual sizing units are made up of a plurality of hollow jacket-type components, through which a cooling medium flows so that the heat absorbed by the sizing units from the article is fed from the sizing units via the region of their outer side faces. The disadvantage of this design of sizing units is that it is not always possible for the article to be satisfactorily calibrated in every type of application.
Other shaping devices for extrusion systems are known from patent specifications DE 199 17 837 A1 and DE 297 16 343 U1 filed by the same applicant, and consist of at least one calibration device comprising in particular a plurality of calibration dies disposed one after the other in the direction of extrusion, this calibration device and/or the calibration dies being provided with cooling ducts through which a coolant is circulated. The calibration device also has shaping surfaces to which an article conforms as it is fed through, a sealing device being provided at least between the extrusion tool of the shaping apparatus, such as a nozzle for example, and the first calibration die immediately following it in the extrusion direction, to form a cavity which seals off the outer surface of the article from the ambient pressure as it is fed through. However, this sealing arrangement for forming an additional cavity may also be arranged between the first calibration die and at least one other calibration die. These calibration dies are designed in a block construction and it is not always possible for the article to be satisfactorily calibrated in every type of application using this design.
Shaping apparatus is also known in which the plastic lengths of sections, in particular hollow sections or tubes, are calibrated to the desired external and internal dimensions as they leave an extrusion nozzle and are frozen to the desired external dimensions or cooled to the requisite temperature to produce the desired rigidity. Shaping systems of this type are described in the book, xe2x80x9cExtrusionswerkzeuge fxc3xcr Kunststoffe und Kautschukxe2x80x9d by Walter Michaeli, published in 1991 by Carl Hanser Verlag, Munich/Vienna, 2nd completely revised and extended version, in particular pages 321 to 329. Page 323 provides an illustration of an external vacuum calibration system, whereby the extruded material leaving the extrusion die in the form of a hollow section is fed into a calibration die at a distance from the point at which it leaves the nozzle lip of the extrusion apparatus, through which extruded material is fed so that the region of its peripheral external surface conforms to the shaping surfaces of the calibration die. The surface of the extruded material is able to engage on the individual shaping surfaces of the calibration die without any clearance due to air inlets, in particular slots, in the shaping surfaces, which communicate via supply lines with a vacuum source. In order to cool the extruded material, the calibration dies are provided with one or more peripheral passages for a cooling medium and the vacuum can be increased in the individual air inlets or slits the farther away they are in distance from the nozzle lip of the extrusion apparatus. The temperature of the cooling medium is very low compared with the mass temperature of the extruded section and is approximately 20xc2x0 C. In so-called dry calibrators of this type, it is common practice to provide one or more cooling baths, in which the sufficiently rigid sections are cooled to ambient temperature, partly by applying a vacuum and wetting using spray nozzles or by passing them through water baths. With calibration apparatus of this type, it is not possible to obtain a sufficiently high surface quality on the finished extruded material in many cases once the shaping device has been in service for any length of time.
The underlying objective of the present invention is to propose a shaping apparatus, in particular a calibration system, by means of which the article being fed through is uniformly and rapidly cooled by virtually the entire circumference of the calibration orifice.
This objective is achieved by the invention with a shaping apparatus for an extrusion system with at least one calibration device comprising means for dispersing heat and at least one calibration die with several calibration units disposed one after another in an extrusion direction. Each calibration unit has at least one calibration orifice with several shaping surfaces which come into contact with an article fed therethrough, end faces spaced apart from each other in the extrusion direction, and side faces extending between the end faces, a first end face being directed towards an inlet region and a second end face being directed towards an outlet region of the article fed through the calibration orifice. At least one cavity is formed between two immediately adjacent calibration units, the cavity extending from a respective one of the shaping surfaces to, and opening into, a passage. The calibration orifice is provided with at least one continuous circulation passage around a predominant part of, and immediately adjacent to, the circumference thereof, the circulation passage having a separate inlet and outline line, extending across a predominant distance of a thickness between the two end faces of the calibration unit and being closed in the region of the end faces, the circulation passage is provided with at least one transverse passage along the circumferential extension thereof extending across a predominant distance of the thickness between the end two faces, the transverse passage being closed at the region of the two end faces and having a flow connection to the circulation passage via at least one connecting passage, and a baffle system projects from the connecting passage in a direction opposite the calibration orifice, at least in certain regions, into the flow cross-section of the circulation passage.
The surprising advantage of this solution resides in the fact that every calibrating unit or units is provided with a separate circulation passage in the region of the calibration orifice, which runs inside the calibration unit without any connection to a delimiting external face thereof other than the inlet and outlet lines. Consequently, virtually the entire circumference of the calibration orifice can be cooled by the coolant fed through the circulation passage. It can be arranged immediately along and adjacent to the shaping surfaces, and the cavities provided between the end faces of immediately adjacent calibrating units can be designed so as to run around almost all or all of the circumference of the calibration orifice. Furthermore, heat is fed away from virtually the entire thickness of the calibration unit in the region of the shaping surfaces because the circulation passage can be disposed right in the region of the two end faces spaced at a distance apart from one another. Also, in areas of the profiled section which are difficult to cool and calibrate, particularly areas where there are groove-shaped recesses, a sufficient quantity of heat can be dispersed from the article in these regions, whilst the closed passage arrangement inside the individual calibration units is preserved. A large amount of heat can also be easily removed from these profiled areas by branching a part-flow off from the main flow of the circulation passage. Furthermore. the partial amount of part-flow diverted from the main flow of the circulation passage and circulated through the transverse passage can be specifically selected to produce a specific cooling result and hence a specific instant which this profiled section solidifies.
If each calibration unit has at least one separate circulation passage, heat is dispersed from the article to the circulating medium uniformly across the entire length of the calibrating device, thereby ensuring that the article is cooled rapidly. The fact that several of the calibrating units are each provided with at least one circulation passage means that it is possible to apply coolant to each of the calibration units separately, enabling heat to be fed away rapidly. Sufficient cooling medium is delivered to each of the calibrating units arranged immediately one after the other to absorb the heat, which means that a large amount of heat can be dispersed from the article.
Preferably, the calibration orifice in each calibration unit has several circulation passages separated from one another, each having separate inlet and outlet lines. Because several separate circulation passages are provided, a higher quantity of cooling medium at a lower temperature can be fed around and along the circumference of the calibration orifice to absorb the heat so that the heat can be carried away even more rapidly.
When the outlet line from a first calibration unit is connected to the inlet line, the circulation passages of several calibration units disposed immediately one after the other can be placed in flow connection with one another to provide a circulation through these passages, so that several calibration units can be equipped to allow the cooling medium to flow in an immediately consecutive arrangement in a simple and uncomplicated manner. This means that a counter-flow circulation can be set up within the individual circulation passages between the calibration units arranged immediately one after the other.
The connection between the outlet line and the inlet line of immediately adjacent calibration units may be disposed externally of the cavity therebetween. In this case, the circulation passages arranged immediately adjacent to one another allow heat to be fed away rapidly from the region of the shaping surfaces on the one hand, and, on the other, the cavity provided around the calibration orifice can be without any connecting line so as to be free for the purpose of applying a vacuum pressure to the external surfaces of the article to be calibrated. This enables a vacuum pressure to be built up unhindered across virtually the entire cross section and external surface of the article.
If the inlet line is connected to the circulation passages by a common distribution passage extending continuously through several calibration units and dispersed externally to the cavity therebetween, the coolant can be distributed to the circulation passages in a simple manner via the common distribution passage arranged upstream of and between them. A vacuum can also be generated unhindered on the external surface of the article across its entire cross section in the region of the cavity.
If several circulation ,passages are connected to the outlet line via a common collection passage extending continuously through the calibration units externally to the cavity therebetween, the individual circulation passages are linked by a common collection passage and the discharge line also provides a simplified means for discharging the coolant fed through the calibration units. Another advantage is that by providing the calibration units with end faces of a planar, design, there is no need to provide sealing elements and the cooling medium can be fed from the circulation passages as far as the collection passage and through it between the individual calibration units in a simple manner.
A uniform flow of the coolant inside the circulation passage is produced if the circulation passage has substantially the same flow cross section and passage dimensions around its circumferential extension around the calibration orifice.
Heat is carried away from the article by the cooling medium uniformly and rapidly if a delimiting surface of the circulation passage facing the calibration orifice runs at a substantially same distance from the associated shaping surface of the calibration orifice.
If a first part of the baffle system is designed as an inlet system from the circulation passage into the transverse passage and second part of the baffle system as an outlet system from the transverse passage to the circulation passage, coolant can be selectively fed into and discharged out from the transverse passage from the main flow in the circulation passage.
A part of the main flow can be diverted past the baffle system unhindered so that a specific quantity of the diverted part-flow can be delivered to the transverse passage if a length of the inlet system plus a length of the outlet system in the direction of the thickness of the calibration unit is shorter than the entire depth of the passage dimension of the circulation passage in the same direction.
Preferably, the length of the inlet system plus the length of the outlet system in the direction of the thickness of the calibration unit is the same as the full depth of the passage dimension of the circulation passage in the same direction. In this case, the part-flow from the main flow of the circulation passage can be delivered to and discharged from the entire depth or width of the circulation passage in a specific amount, providing a simple means of obtaining the desired cooling effect and the related dispersion of heat in the region of the transverse passage.
If the inlet system and the outlet system are disposed in the circulation passage respectively adjacent to one of the two end faces, a longitudinal and transverse flow is produced inside the circulation passage between the two end faces spaced at distance apart from one another, thereby avoiding dead spaces inside the individual flow passages and guaranteeing a high dispersion of heat.
Arranging the cavity or several cavities around the entire circumference of the calibration orifice, right up to the shaping surfaces delimiting the calibration orifice, enables a uniformly homogeneous vacuum to be produced across almost the entire periphery of the section. Another advantage is the fact a pressure below atmospheric pressure can now be applied to profiled sections that are difficult to calibrate, which means that perfect calibration results can also be achieved in these regions. Similarly, this uniform pressure differential between cavities in the hollow section and the external surfaces of the article allows the external surfaces of the article to be made to lie so that they almost completely conform to the shaping surfaces, improving the dimensional stability of the article to be produced. The design of the circumferential cavity around almost the entire circumference of the calibration orifice makes manufacture less complicated than the system employed for a block structure arrangement where vacuum slits, and the bores needed to apply a vacuum pressure to the vacuum slits, have to be provided in the calibration blocks.
Preferably, the cavity has a differing width starting from the shaping surfaces in the direction parallel with the shaping surfaces and the width increases the greater the distance from the shaping surface is. Thus is of advantage because the volume of the cavity increases the farther it is away from the shaping surfaces, affording a larger cross section for the intake of air and the process of building up a vacuum pressure, which also means that longer intake paths are provided to compensate for pressure losses, in turn enabling an almost homogeneous vacuum to be generated in the region of the external surface of the article.
Specifically claimed dimensions of the cavity enable a specific flow cross section to be set depending on the selected width of the cavity and, in the immediate transition region between facing end faces of calibration units disposed immediately one after the other, the dimension of the cavity or gap between the end faces can be selected to suit requirements, on the one hand enabling flow losses to be compensated and, on the other, preventing too high suction at surface areas of the article in the region of the vacuum slit.
The width of the cavity may differ around the circumference of the calibration orifice in the region of the first partial end face. This enables the pressure differential between the cavities of the article and its external surface to be set.
The may be fed more efficiently and unhampered into the individual calibration units if a radius in a transition region between the shaping surfaces and the immediately adjacent first partial end faces of the calibration units is between 0.1 mm and 1.0 mm.
Other claimed embodiments of the shaping apparatus bring a considerable reduction to the cost of manufacturing the individual calibration units, because the individual cavities can be made simply by processing the end faces, for example. This significantly improves accessibility, enabling the gap widths in the cross-over region between the individual calibration units to be better adjusted. This also offers a simple and uncomplicated means of evacuating the individual cavities by connecting them to the co-operating vacuum passages.
Finally, the calibration unit is preferably between 6.0 mm and 60.0 mm thick in the direction perpendicular to the end faces, which allows the number of cavities distributed around the calibration orifice to be fixed and varied on the one hand, and, on the other, reduces the processing needed to make the circulation passages.